Check out /r/suggestalaptop?
General comments: SSDs are generally faster than magnetic drives, but often fail much sooner.
If you're not positive you want to replace it altogether: You might be able to fix your heat/slowness issues just by taking a can of compressed air to it. And you could probably buy a new battery. Replacing it might still be a better proposition overall, though...
Source on SSDs failing sooner? I thought (or assumed) it was the opposite. A quick Google search turns up the headline "SSD Annual Failure Rates Around 1.5%, HDDs About 5%".
Looking further, though, I also see: "An SSD failure typically goes like this: One minute it's working, the next second it's bricked.". The page goes on to say that there's a service that can reliably recover the data from a dead drive, but that seems like a privacy concern (if everything on the drive weren't logged by the NSA to begin with).
On the pro-SSD side, thou...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.